1. Field of the Invention
The present invention relates to a rotor for an automotive alternator, which has a Lundell-type core, for mounting on an automobile engine, and in particular, relates to a winding configuration for winding onto the Lundell-type field core.
2. Description of the Related Art
FIG. 2 is a cross-section of a conventional rotor for an automotive alternator and FIG. 3 is a cross-section of part of the rotor shown in FIG. 2.
In FIGS. 2 and 3, a rotor 1 comprises a rotating shaft 11 rotatably supported by a pair of brackets (not shown), a pair of Lundell-type field cores 12a, 12b secured to the rotating shaft 11, a pair of fans 13a, 13b secured to both axial ends of the field cores 12a, 12b, slip rings 14 secured to one end of the rotating shaft 11, and a field winding 15 wound onto the field cores 12a, 12b.
The field cores 12a, 12b are made of iron, comprise cylindrical base portions 121a, 121b fitted over and secured to the rotating shaft 11 and claw-shaped magnetic poles 122a, 122b plurally projecting from the outer circumferential edges of the base portions 121a, 121b, and are secured to the rotating shaft 11 facing each other such that the end surfaces of the base portions 121a, 121b are in close contact with each other and the claw-shaped magnetic poles 122a, 122b intermesh alternately. The field winding 15 is a copper wire with a flat shape having a rectangular cross-section and is wound a predetermined number of times onto a bobbin 16 fitted over the outer circumferences of the base portions 121a, 121b. A magnetic flux is generated when an electric current is supplied to the field winding 15 by means of the slip rings 14 and magnetic poles are formed in the field cores 12a, 12b by the magnetic flux.
Inner circumferential tape 17a for protecting the winding is wound onto the cylindrical portion 16a of the bobbin 16. Outer circumferential tape 17c for protecting the winding is also wound onto the outer circumference of the field winding 15 wound onto the bobbin 16. In addition, side tape 17b is disposed between the lead portion of the field winding 15 and the multi-layered portion of the field winding 15.
The construction of the field winding 15 will now be explained with reference to FIG. 4.
The bobbin 16 is made of resin, and comprises a cylindrical portion 16a and a pair of first and second annular flange portions 16b projecting perpendicularly from both ends of the cylindrical portion 16a. A recessed groove 161 for housing a lead wire 15a at the start of the winding is disposed at an angle with respect to the radial direction in the inner surface of the first flange portion 16b so as to extend from the outer circumferential side thereof to the cylindrical portion 16a. An anchor portion 16c is disposed on an outer circumferential portion of the first flange portion 16b in close proximity to the upper end of the recessed groove 161.
First, the inner circumferential tape 17a is wound onto the cylindrical portion 16a of the bobbin 16. Then, the starting portion of the field winding 15 is wound around the anchor portion 16c, inserted into the recessed groove 161, and drawn from the lower end (inner circumferential end) of the recessed groove 161 onto the cylindrical portion 16a. At this point, the side tape 17b is pasted onto the inner surface of the first flange portion 16b so as to cover the lead wire 15a at the start of the field winding 15 which is housed in the recessed groove 161. Then, the field winding 15 drawn out onto the cylindrical portion 16a is lined up in rows at an angle relative to a plane which perpendicularly intersects the axial center of the bobbin 16 as it is wound onto the cylindrical portion 16a. Then, when the first layer of the winding is finished, a second layer is lined up in rows at an angle relative to the plane which perpendicularly intersects the axial center as it is wound onto the cylindrical portion 16a. In this way, the field winding 15 is wound up layer by layer in order from the bottom of the cylindrical portion 16a, and when a predetermined number of layers have been wound, the outer circumferential tape 17c is wound onto the outermost circumferential portion. In addition, the multi-layered portion of the field winding 15 is saturated with varnish.
The starting portion of the field winding 15 will now be explained.
The broad surface of the flatly shaped lead wire 15a is housed in the recessed groove 161 so as to closely contact the bottom of the recessed groove 161. In other words, the broad surface of the lead wire 15a lies on a plane which intersects the axial center of the bobbin 16 perpendicularly. The outer circumferential surface of the cylindrical portion 16a of the bobbin 16, on the other hand, is parallel to the axial center of the bobbin 16.
Thus, the field winding 15, whose broad surface lies on a plane which intersects the axial center of the bobbin 16 perpendicularly, is bent at a right angle towards the cylindrical portion 16a at the inner circumferential end of the recessed groove 161, and is drawn out onto the outer circumferential surface of the cylindrical portion 16a. In addition, the field winding 15 drawn out onto the outer circumferential surface of the cylindrical portion 16a is twisted at approximately 90 degrees on the outer circumferential surface of the cylindrical portion 16a such that the longitudinal direction of the field winding 15 is at an angle relative to a plane which intersects the axial center of the bobbin 16 perpendicularly, and winding of the first layer is started.
In the conventional rotor 1 for an automotive alternator constructed in this manner, in the starting portion of the fieldwinding 15, the field winding 15 is bent at a right angle towards the cylindrical portion 16a at the inner circumferential end of the recessed groove 161, and is drawn out onto the outer circumferential surface of the cylindrical portion 16a, and in addition is twisted at approximately 90 degrees on the outer circumferential surface of the cylindrical portion 16a such that the longitudinal direction thereof is at an angle relative to a plane which intersects the axial center of the bobbin 16 perpendicularly. However, the field winding has a flat shape and therefore cannot completely absorb the kinks caused by bending and twisting, and kinks arise in the starting portion of the field winding 15.
Thus, one problem is that the second and subsequent layers of the field winding 15 are wound over the kinks, leading to damage in the starting portion of the field winding 15. Furthermore, the starting portion of the field winding 15 is the bottommost layer in the multi-layer portion and damage to the wire is difficult to detect there, leading to quality control problems.
Another problem is that the angle of the bending and twisting of the field winding 15 at the inner circumferential end of the recessed groove 161 is great, reducing workability as well as giving rise to wire breakages.